In this study the effects of pulsed electromagnetic field (PEMF) on pain relief and functional capacity of dogs with osteoarthritis (OA) were investigated, and compared with firocoxib. Patients were randomly assigned to two groups: twenty-five client-owned dogs were treated with PEMF once a day for 20 sessions, and fifteen dogs (control group) were treated with 5 mg/kg of firocoxib once daily for 20 days. Blinded clinical examination and owner’s assessment were recorded before and after the therapy, as well as 4 and 12 months later. Data collections were statistically compared before and after treatments and between groups. Both groups showed decreased clinical signs of OA during the treatment. Compared with baseline, these improvements were statistically significant (P<0.01) during the therapies. Differences were recorded during observation time spans following the end of treatments. In the PEMF group the effects were sustained until the end of the study, whereas in the control group the progress tended to return to baseline values after the end of therapy. The beneficial effects of PEMF on pain relief and functional capacity make it a potential treatment modality for canine osteoarthritis compared to traditional pharmacological therapy, in absence of adverse effects and in favour of the quality of life.